This invention relates to open mesh bags suitable for packaging goods and articles.
Heretofore, open mesh bags have been used for various packaging applications including those in which breathability and visibility of the bags"" contents are important features. Examples include produce bags for fruits, vegetables and other agricultural products and bags for sporting equipment, toys, blocks and various other small to medium size solid objects. Such bags have been made from solid plastic films, tubular packaging materials, such as VEXAR originated by E.I. du Pont de Nemours and Company, leno weave fabrics, knitted fabrics and flat woven fabrics. Each of these has disadvantages. For example, tubular materials require investment in specialty equipment to prepare bags from same (see, e.g., U.S. Pat. No. 4,091,595). Flat weave and knitted packaging materials, while avoiding complexities associated with tubular goods, are disadvantageous because they are typically sewn to form seams. This adds cost. Nonwoven fabrics seldom achieve a practical balance of strength and contents-visibility and they are often difficult to seam with appropriate strength. Plastic films lack breathability; attempts to overcome this limitation, such as by perforation, add cost, can impair strength and generally do not perform satisfactorily.
Beyond traditional attributes of produce bags, including strength, breathability and sufficient transparency or openness to allow viewing of their contents, high speed and automated bagmaking and filling equipment have imposed additional requirements. To process well on high speed bagmaking equipment, bag substrates must track precisely through the equipment and remain in registration over the entire sequence of bagmaking steps. The substrate must remain precisely in registration through repeated accelerations and decelerations so that each step of the bagmaking operation, e.g., seaming, label application, die cutting, finished bag cut-off, is performed in precisely the right position on the bag. Dimensional stability of a bag substrate is important for such operations from the standpoint of maintaining registration and avoiding deformation as the material rapidly starts and stops during its progression through the bagmaking equipment.
The substrate must also be a material that can be seamed with adequate strength to withstand filling operations, transportation and handling. Bags manufactured from open-mesh fabrics can be problematic in this respect, particularly those that comprise a delicate, net-like material and/or have only limited surface area available for seaming. Limited area for contact between opposite layers of the fabric tends to make heat sealed seams weak, if effective at all. Seaming with adhesives tends to be aesthetically unattractive. Sewn seams add cost and are often ineffective due to the small surface area of the open mesh fabric.
U.S. Pat. No. 3,123,279 discloses a plastic open-mesh bag having a thermoplastic film joined to a thermoplastic net along three margins of the film made by folding the film over the net and sealing the film through the net.
There remains a need for improved open mesh bags, and particularly bags that have the traditional attributes of conventional open mesh bags, such as breathability and contents-visibility, and also meet the criteria for high speed bagmaking machines.
Briefly, this invention provides a bag comprising an open mesh fabric and having a closed, butt end, an opposing end, and at least two longitudinal seams extending from the butt end to the opposing end, wherein the butt end is formed by a fold in the fabric on a central axis and each seam comprises a section of fabric from each side of the fold to which is heat sealed a thermoplastic sealing strip. The thermoplastic sealing strip to which the fabric is sealed comprises a thermoplastic resin or blend of resins having a melting temperature or heat seal temperature lower than the melting temperature of the fabric. Optionally, a label, print band or other decorative elements can be affixed to the bag.
Importantly, the inventive open mesh bags can be manufactured with ease on industrial high speed automated bagmaking equipment. Heat-sealable film strips comprising a thermoplastic resin are preferably applied by lightly heat sealing the strips across approximately one half the width of the fabric, preferably in the cross machine direction, so that when the fabric is folded on a central axis the film strip extends perpendicular to the fold and along the full height or length of the bag. In addition, the invented bags are well suited for use in automated bag filling operations owing to their dimensional stability and ability to be wicketed. Significantly, these attributes are achieved without loss of other important features, including strength, flexibility, breathability and contents-visibility.